[Help-glpk] things I don't understand in src/env/time.c + bugs + suggested patch

[David Monniaux]

Over glpk-4.61

src/env/time.c contains:

double glp_time(void)
{     struct timeval tv;
      struct tm *tm;
      int j;
      double t;
      gettimeofday(&tv, NULL);
      tm = gmtime(&tv.tv_sec);
      j = jday(tm->tm_mday, tm->tm_mon + 1, 1900 + tm->tm_year);
      xassert(j >= 0);
      t = ((((double)(j - EPOCH) * 24.0 + (double)tm->tm_hour) * 60.0 +
         (double)tm->tm_min) * 60.0 + (double)tm->tm_sec) * 1000.0 +
         (double)(tv.tv_usec / 1000);
      return t;
}

This code suffers from several problems:
- The division tv.tv_usec / 1000 is integer division, then converted to
double; why not simply multiply by 1E-3, which is more precise?
- It uses gmtime, which is not reentrant (as opposed to gmtime_r). In
fact, my attention was called to this function because of error reports
by Valgrind's DRD race condition analyser ran on code using glpk from
different threads.

I also do not understand why it is useful to use such a function,
calling jday() to convert Julian days, whereas the following returns the
same result:

double glp_time(void)
{     struct timeval tv;
       gettimeofday(&tv, NULL);
      return tv.tv_sec + 1E3 * tv.tv_usec * 1E-3;
}

What am I missing?

If I'm missing nothing, this patch simplifies the code:

--- glpk-4.61-orig/src/env/time.c    2017-01-22 08:00:00.000000000 +0100
+++ glpk-4.61-time-patched/src/env/time.c    2017-01-28
13:09:07.367464607 +0100
@@ -53,17 +53,8 @@
 
 double glp_time(void)
 {     struct timeval tv;
-      struct tm *tm;
-      int j;
-      double t;
       gettimeofday(&tv, NULL);
-      tm = gmtime(&tv.tv_sec);
-      j = jday(tm->tm_mday, tm->tm_mon + 1, 1900 + tm->tm_year);
-      xassert(j >= 0);
-      t = ((((double)(j - EPOCH) * 24.0 + (double)tm->tm_hour) * 60.0 +
-         (double)tm->tm_min) * 60.0 + (double)tm->tm_sec) * 1000.0 +
-         (double)(tv.tv_usec / 1000);
-      return t;
+      return tv.tv_sec + 1E3 * tv.tv_usec * 1E-3;
 }
 
 /* MS Windows version *************************************************/
@@ -92,17 +83,7 @@
 #include <time.h>
 
 double glp_time(void)
-{     time_t timer;
-      struct tm *tm;
-      int j;
-      double t;
-      timer = time(NULL);
-      tm = gmtime(&timer);
-      j = jday(tm->tm_mday, tm->tm_mon + 1, 1900 + tm->tm_year);
-      xassert(j >= 0);
-      t = ((((double)(j - EPOCH) * 24.0 + (double)tm->tm_hour) * 60.0 +
-         (double)tm->tm_min) * 60.0 + (double)tm->tm_sec) * 1000.0;
-      return t;
+{      return time(NULL) * 1E3;
 }
 
 #endif

Regards
-- 
David Monniaux
directeur de recherche au CNRS, laboratoire VERIMAG
Université Grenoble Alpes
http://www-verimag.imag.fr/~monniaux/

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